Builder&#39;s hoist



Nov. 24, 1964 M. GRUNFELD 3,157,997

BUILDER'S HOIST Filed Nov. 8, 1962 4 Sheets-Sheet l lau ummlumlllul as v ;{99

as ea MICHAEL GRUNFELD F I 6.4. INVENTOR.

BY l V m I mlw ATTORNEY Nov. 24, 1964 M. GRUNFELD 3,157,997

BUILDER'S HOIST Filed Nov. 8, 1962 4 Sheets-Sheet 2 F l G. 5. F l G. 6. BLOCKED FLOW VALVED CRACKED rianmrimnv/aiw FIG.I2.

R REL VALVE -r0 as re TANK ATTORNEY Nov. 24, 1964 M. GRUNFELD 3,157,997

BUILDER'S HOIST Filed Nov. 8, 1962 4 Sheets-Sheet s 65 FLOW LIMITING MEANS MICHAEL GRUNFELD INVENTOR.

ATTORNEY Nov. 24, 1964 M. GRUNFELD BUILDER'S HOIST 4 Sheets-Sheet 4" Filed Nov. 8, 1962 FIG. l5.

Fl G. I50.

FIG. l5b

FIG. I4.

MICHAEL GRUNFELD INVENTOR.

BYW

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ATTORNEY United States Patent 3,157,997 BUILDERS HGXST Michael Grunfeid, Los Angeles, Caliii, assignor to Tubular Structures Corp. of America, Los Angeles, Calif., a corporation of California 7 Filed Nov. 8, 1962,: Ser. No. 236,248

6 Claims. (Cl. 60 -53) The present invention relates generally to hoisting equipment and elevators and more particularly to a portable hoist adapted for lifting and lowering materials in the course of constructing or razing buildings. It will be realized from the description to follow that the invention herein described is not limited to the specific embodiments shown and described but will have application in other allied fields. The hoist described in this application is an improvement over the hoist described in Patent No. 2,869,325, issued January 20, 1959, and Patent No. 3,036,435, issued May 29, 1962, to Max Samuely. However, the hoist irr many respects is substantially similar to the hoist described in the said aforementioned patents so their disclosures are hereby incorporated in this application.

Devices of the type generally described above have been available in the past but have been subject to a number of disadvantages. Previously known hoists of this general type consist of a tower having vertical guides, a platform engaged with the guides, and a simple winch for raising or lowering the platform along the guides.

Prior to the present invention, portable hoists in general use with the notable exception of the aforementioned Samuely hoists have not been designed for rapid and efficient use in that they have not incorporated means for accelerating and decelerating the platform travel at the beginning and end respectively of their movement up and down the tower guides. However, even where such accelerating and decelerating means are available such as in the Samuely hoist, a hydraulic motor acting as a pump has been utilized to regulate the rate of down-travel of the platform rather than a mechanical friction brake. Such utilization of a motor as a pump for a brake set definite limits on the rate of downtravel of the platform; particularly, where a flow regulator was utilized in the outlet of the hydraulic motor-pump. Consequently, particularly in the case of tall buildings, relatively inelficient slow rates were obtained during the down travel portion of the operation of the hoist.

Another difiiculty encountered in the hoists of the type described which have been available heretofore, is the fact that they are normally transported in a compact closed position, i.e., the base frame and the frame-work tower portions of the hoist are collapsed together and require positioning at the job site. Such positioning in the prior art was normally done manually and involved considerable labor and time.

Bearing in mind the foregoing difliculties, it is a major object of the present invention to provide a portable power hoist of the class described in which a speed substantially equal to free fall is obained during the downtravel portion of the hoist operation.

Another object of the present invention is to provide a portable power hoist equipment of the class described in which the frame-work tower portions may be erected by power means rather than manually.

Another object of the present invention is to provide a portable power hoist incorporating the aforesaid objects and also having relatively high speeds of up and down travel which may be obtained without attendant shocks at the beginning and end of such travel.

Another object of the present invention is to provide portable power hoisting equipment in which the speed of up and down travel may be adjusted over a relatively wide range for various applications.

Another object of the present invention is to provide an improvement wherein the automatic flow restricters provided in the hydraulic connection to the motor-pump unit may be bypassed to provide an increased rate of down travel.

The foregoing and additional objects and advantages of the invention will be apparent from the detailed description to follow, consideration being given to the accompanying drawing in which:

FIG. 1 is an elevational view of a portable bu-i-lders hoist embodying the present invention, the same being shown in a travelling position;

FIG. 2 is a fragmentary side elevational view of the hoist shown in FIG. 1 in an erected position ready for operation;

FIG. 2a is an enlarged horizontal section taken on the line 2a-2a of FIG. 2;

FIG. 3 is a fragmentary elevational view partially sectioned, showing a first form of hydraulic control valve and operating cam embodied in the hoist shown in FIGS. 1 and 2;

FIG. 4 is an elevational section taken on the line 44 in FIG. 3;

FIGS. 5, 6, and 7 are sequential semi-schematic views of a second form of hydraulic control valve and operating cam which may be embodied in the hoisting equipment shown'in FIGS. 1 and 2;

FIG. 8 is an actual section of a uni-directional, constant flow regulator incorporated in various of the control systems embodied in the present invention;

FIGS. 9, l0 and 11 are hydraulic circuit diagrams schematically illustrating the operation of certain forms of the invention during the up-travel, stop, and downt-ravel conditions respectively;

FIGS. 12 and 13 are fragmentary schematic views of a prime mover throttle control system of the system shown in FIGS. 10 through 12 showing respectively, open and closed throttle positions;

FIG. 14 is an enlarged sectional view of the flow limiting means in the conduit between the reservoir and hydraulic motor shown schematically in FIGS. 9, 10 and 11;

FIG, 15',- 15a, 15b and 15c are hydraulic circuit diagrams schematically illustrating the operation of the tower positioning means and assoicated valve means during the raising, stop, down and lowering conditions respectively.

In general, the power hoist system ofthe present invention includes'a hydraulic pumpSl and a reservoir or storage tank 52 forhydraulic fluid connected to' the hydraulic pump 51 by conduit means. A hydraulic motor 53 is connected to the reservoir 52 by conduit means. Conduit means connect the hydraulic pump 51 and motor 53 including a first valve means The first valve means S5 is connected by conduit means to the reservoir 52 and has an up position for raising the hoist 30 in which the hydraulic pump delivers pressurized hydraulic fluid to the hydraulic motor 53. The first valve means 85 also has a down position for lowering the hoist 30 in which the hydraulic motor 53 acts as a pump delivering hydraulic fluid to the reservoir 52 through the first valve means 85. One improvement of the present invention includes a flow limitingmeans 269 in the conduit between the reservoir 52 and the hydraulic motor 53 which is adapted to restrict the flow of hydraulic fluid to the hydraulic motor 53 when the first valve means 85 is in a down position to an amount sufficient to lubricate the hydraulic motor 53 but insufiicient to prevent the hoist'30 from coming down at a rate of sub'stantially'free fall. Also the present invention includes a positioning means 210 for raising and lowering hoist 3t) to and front a vertical position and a third valve means 220 for controlling said positioning means. Positioning means 210 is connected through the third valve means 220 by conduits between the hydraulic pump 51 and the reservoir 52. Another improvement of the present invention is a second valve means 232 in a parallel conduit between said first valve means 85 and the hydraulic motor 53 which is adapted to permit free flow from the hydraulic motor 53 to the first valve means 85.

The portable builders hoist embodied in the present invention is indicated in the drawings generally by the the reference character and comprises a frame-work tower 31 having longitudinal guide rails 32 on a forward face thereof, a load carrying platform 33 mounted for sliding movement along the rails 32 and a draw-works 34 incorporating a winch drum 35 having a hoisting cable 36 reeved through the conventional sheaved means shown generally at 37 whereby to raise and lower the platform 33. The hoist 30 includes base frame 40 having suitable ground engaging pads 41 and 42, the entire structure being mounted on a pair of trailer wheels 43 whereby the hoist 30 may be drawn behind a towing vehicle being attached by conventional trailer attachment means (not shown) at the upper end 44 of the tower 31.

When it is desired to lower the tower 31 from the operative position shown in FIG. 2 to the travelling position shown in FIG. 1, the rear-most ground engaging pads 42 are retracted lowering the wheels 43 to the ground. The tower 31 is then tilted rearwardly (counterclockwise in FIG. 2) about a horizontal pivot axis at 45 by retracting the piston rod 211 attached to the frame-work tower 31 and piston 212 in the cylinder 213 until the tower rests against the abutments 46 connected to the carriage (not shown) supporting the wheels 43. The reverse procedure is utilized to position the tower 31 to the operative position from the travelling position.

Power to operate the hoist 30 is derived from a prime mover 50, in the present case, an internal combustion engine. As may be seen in FIGS. 9 through 11, prime mover 50 is mechanically connected to the hydraulic pump 51 which may be any type of relatively high pressure pump preferably of the positive displacement type such as a gear pump, vane pump, or the like. The pump 51 derives its fluid from a reservoir or storage tank 52 and delivers it to through control means to be determined in more detail later herein, to a hydraulic motor 53'which is preferably of the positive displacement type. The hydraulic motor 53 is mechanically connected to drive the winch drum 35 to wind the cable 36 thereon and lift the platform 33.

A spring-held pressure suspended friction brake 55 is operatively associated with the winch drum 35 and fluidconnected to the hydraulic system whereby the drum 35 is held stationary by a brake shoe 56 forced into contact therewith by the compression spring 57 except where there is operative hydraulic pressure in a high pressure conduit 58 as will be described. Pressure in the conduit 58 forces fluid into the upper end of an actuating cylinder 59 causing a piston 60 to draw downwardly on the brake shoe 56 releasing the same from the drum 35 permitting the latter to rotate. The compressive force of the spring 57 is suflicient to hold the drum 35 stationary with the platform 33 in a raised position and with the maximum permissible load thereon. The brake 55 is used only to lock the platform in a desired position. It is not used to slow the down-travel of the platform 33. Other means are provided for the latter purpose as will be explained.

The hydraulic pressure system also includes a conduit 62 leading to an actuating cylinder 63 having a piston 64 therein mechanically connected to a throttle lever 65 which controls the speed of the prime mover 50. A compression spring 66 normally urges the throttle lever 65 upwardly, i.e., in a closed throttle direction. The open throttle and closed throttle conditions are illustrated in FIGS. 12 and 13 respectively. From the foregoing, it will be seen that when there is no pressure in the conduit 62 the spring 66 closes the throttle of the prime mover 50 and the same idles. When pressurized fluid is introduced through the conduit 62 into the actuating cylinder 63, however, the piston 64 moves downwardly opening the throttle and speeding up the operation of the prime mover 50 thus increasing the power delivered to the pump 51.

In all of the forms of the invention herein described, the hydraulic motor 53 reverses its function during the down-travel of the platform 33, the latter causing the cable 36 to unwind from the drum 35 and this unwinding rotation of the drum 35, in turn driving the motor 53 backwardly causing the same to pump fluid. Speed of the down-travel of the platform 33 may therefore be controlled by restricting the flow from or to the hydraulic motor 53 (now acting as a pump).

Restriction of the flow from the hydraulic motor 53 during the down-travel of the platform 33 is affected by an adjustable flow regulator 68 (see FIGS. 9-11) which takes the form of a uni-directional flow regulator, a construction of which is shown in FIG. 8. In the device shown in FIG. 8, flow regulation takes place not only when the flow is from the motor 53, i.e., through the device in a direction entering at the conduit 69 and leaving at the conduit 70 but also when the flow is in the reverse direction. The first flow direction is indicated by the arrow in the conduit 69 in FIG. 8 and it will be seen that as the fluid passes this direction into a chamber 71, in the regulator 68, a restricted orifice 72 in a slidable piston valve member 73 therein, causes pressure to build up in the chamber 71 urging the piston 73 to the left against the yielding resistance of a spring 74. The resistance of the spring 74 may be adjusted by an abutment screw 75 by which the initial stress on the spring 74 may be varied. As the piston 73 moves to the left, the skirt thereof passes across an exit point 77 leading to the conduit 70 and thus causes an additional restriction to flow through the entire regulator 68. For any given pressure, the increased restriction at the port 77 decreases the rate of flow through the regulator 68. As such flow must all pass through the orifice 72, the decrease in rate of flow decreases the pressure drop through the orifice 72 and thus permits the spring 74 to move the piston 73 to the right tending to open the port 77. When these two opposing force reach a condition of equilibrium, the rate of fluid flow through the regulator 68 reaches a certain relatively constant value and it will be seen that this value is substantially the same irrespective of the pressure at the conduit 69. Thus the maximum speed at which the motor 53 may be driven by the pump 51, during the down-travel of the platform 33, is limited when there is unrestricted hydraulic fluid flow to the motor 53 to that which produces the limited flow rate through the regulator 68, when regulator 68 forms the sole control between the motor 53 and the valve 85.

Where unrestricted flow to the motor 53 is permissible and maximum down speed of the platform 33 is desired, a parallel conduit 231 and a gate valve 232 may be used to connect the hydraulic motor 53 to the first valve means 85. The gate valve 232 may be of any convenient type such as the handle-operated gate valve illustrated in FIG. 14 except that a solid block is used in place of the one containing the aperture illustrated therein. When gate valve 232 is open, flow from motor 53 is relatively unrestricted to the first valve means so that the downspeed is limited only by the pumping action of the motor.

However, the maximum possible downspeed of the platform 33, is, of course, a speed which is substantially equal to free fall of the platform 33. Such maximum down speed may be obtained by use of a flow-limiting means 200 in the conduit 53 between the reservoir 52 and the hydraulic motor 53. In the present invention, the flow limiting means 200 is adapted to restrict the flow of hydraulic fluid to the hydraulic motor 53 when the first valve means 85 is in a down-position to an amount sufficient to lubricate hydraulic motor 53 but insufficient to prevent the hoist 30 fromcoming down at a rate of substantially free fall. Thus, the flow limiting means 200 may comprise a gate valve 201 as illustrated in FIG. 14 operated by a handle 202 betweena fully opened and a fully closed position. The block portion 203 of the gate valve 201 includes a small aperture 204 which permits a suflicient amount of hydraulic fluid to be pumped by the motor 53 so as to lubricate motor 53 when the value 201 is in a closed position. However, the pumping action of the motor 53 on such small amount of hydraulic fluid causes intense cavitation and foaming without creating any resistance to the free motion of the motor parts so that the motor 53 is lubricated and permits the hoist to come down at a rate of substantially free fall.

In order to prevent the damage to the pump 51 or the hydraulic motor 53, in the event of a malfunction in the control system causing abnormal flow through these devices, each is connected by a high-pressure release valve to the reservoir 52. A high-pressure release valve for the pump 51 is indicated in the drawings at 80 and that for the hydraulic motor 53 is indicated at 81.

As thus far described, it will be seen that the control of the platform 33, whereby it is caused to move upwardly or downwardly as desired, is accomplished by connecting the pump 51 to deliver pressure to the hydraulic motor on the one hand or alternatively connecting the output of the motor 53' to the reservoir 52 through the flow regulator 68 to restrict the fluid flowing from the hydraulic motor 53 or through the second valve means 232 to permit free flow to the hydraulic motor 53. These selective connections are accomplished by means of a master control valve which in the form illustrated in FIG. 3 is a 4-way three-position spool valve. The flow limiting means 200 between the reservoir 52 and the hydraulic motor 53 is operated seperately.

The internal construction of the valve 85 is more or less conventional and is illustrated in FIG. 3 wherein it will be seen that the pressure fluid introduced at a conduit 86 may be selectively connected through internal passages in the valve to a tank connection conduit 87; motor connection conduit 71), or an alternate return conduit 88. Selective inter-connection as just described is accomplished by moving a spool member 89 axially within the body of the valve85 in one direction or the other from a central position in which it is held by centering spring assembly illustrated at 90.

Inasmuch as the specific details of the four-way open center valve 85 employed in the present invention are conventional, and inasmuch as invention does not reside in the particular design of the valve itself, no further detail description is deemed necessary herein. Suffice it to say, that when the spool 89 is moved to its righthand limiting position (e.g., FIG. 9) pressure fluid from the conduit 86 is connected to the conduit 70. When spool 89 is centered (e.g., FIG. 10) fluid from the conduit 86 may flow unrestricted through the conduit 87 to the reservoir 52.

Interposed in the return conduit 83 between the control valve 85 and the reservoir 52, is a low restriction valve relief 95 the purpose of which is to maintain some pressure in the conduit 58 even when the valve 85 is in position to return fluid pressure through the conduit 88 to the reservoir 52. This pressure in the system is required during down travel as can be seen in FIG. 11 in order to hold the brake shoe 56 away from the drum 35 so as to permit down-travel of the platform 33 and also to permit maintenance of pressure in the conduit 62 so as to open the throttle of the prime mover sufllciently so that it may drive pump 51 at aspeed so as to produce the pressure necessary to hold the brake off.

At this point, it should be noted that the system fails safe that is, in the event of a failure of the prime mover or any part of the hydraulic system, the pressure is released from the brake actuating cylinder 59 or never build up therein, thus keeping the brake on and prevent ing operation of the system until the failure is corrected.

Movement of the spool 89 back and forth from its spring-centered position, in the body of the valve 85, is effected by a rotary cam system mounted on a shaft 96 and adapted to engage one or the other of two cam follower rollers 97 and 98 which are in turn mounted on a common slide member 99 connected through a connecting rod 160 to the spool 89.

In one form of the device illustrated in full line in FIG. 3, the finger-like cam 1.1)1 (shown in full line in FIGS. 9ll) is employed having a relatively restricted cam surface 1th? adapted to contact the rollers 97 and 98 only at or near the ends of its 180 rotary movement. In this form, a dashpot 102 is operatively associated with the connecting rod 1% whereby to damp the motion of the spool 89 returning to its center position from either its left-hand or right-hand limited positions. That is, assuming that cam 1111 has been rotated to its limiting position clock-wise thus contacting the cam follower roller 98 and moving the spool 89 to its extreme righthand position and assuming that the cam 1111 is thereafter rotated to a centralized position as illustrated in full line in FIG. 3, the spool 89 will return to its central position under the urging of the centering spring assembly 90. The spool will, however, return somewhat slowly due to the damping action of the dashpot 1112' wherein a piston 193 causes fluid on one side thereof to pass through a restrictive orifice 104 and a passage 105 to the other side of the piston 1113. The restriction of the orifice 1114 may be adjusted by a needle valve 106. The purpose of this arrangement will be described later herein.

As can be seen in FIG. 2, the cam shaft 96 is mounted on a common base with the winch-drum 35 and prime mover 50 is drivingly connected through sprocket chains 114i and 111 to a control cable drum 112. Two sprocket chains and 111 are employed and engage separate sprockets on a common shaft coaxial with the pivot axis at 45 whereby the raising and lowering of the tower 31 does not interfere with or disturb the driving action between the cam shaft and the cable control drum 112. Provision for manual as well as automatic operation of the master control valve 85 is made in the form of a control cable mounted on a pair of drums or pulleys, the

lower one of which is the control drum 112 and the upper one of which indicated at 116, is mounted at the upper end of the tower 31 whereby to provide a length of control cable at 117 which is parallel to and closely adjacent the platform guides 32. Clamped to the cable 115 at appropriate points along the length 117 are two stop members 118 and 119 conventionally referred to as eggs. As can be seen in FIG. 2, the platform 33 is provided at its rearward edge with a pair of vertically extending slide members 1213 adapted to engage the guides 32. At the upper end of one of the slide members 124 is a closed fork 121 which is positioned to bracket the cable length 117 as can be seen in FIG. 2a.

It will be seen that as platform 33 reaches either its upper or limiting positions in its travel along the tower 31, the fork 121 engages one or the other of the eggs 118 and 119 thus moving the cable 115 and rotating the control drum 112. The rotary motion of the control drum 112 is transmitted through the previously described sprocket chain connection and cam to the valve spool 89 thus changing the position thereof. The just described control cable-sprocket chain connection to operate the valves is common to all of the forms of the invention illustrated herein. It should be noted that the flow-limiting means 2% may bealso'controlled by a similar control cablesprocket chain connection from the platform 33, if desired.

As has been previously described the normal position of the valve spool 8%, when not influenced by the earn 101, is in the centerof its movement in the body of the valve 85. When in this position, as shown in full line in FIG. 3, and as indicated schematically in FIG. 10, pressure fluid entering at 86 is transmitted directly through the valve withoutsubstantial resistance and returned to the tank 52 through return conduit 87. Thus there is no resistance in the flow of fluid in the manner just described, substantially no pressure is developed in the conduit 58 and thus brake shoe 56 remains against the drum 35 and the throttle 65 remains in idling position. The normal or non-operating position of the cam 101 is shown in full line in FIG. 3 wherein it will be seen that the cam is midway between the cam followers 97 and 98 and out of contact with the same.

As illustrated in FIG. 15, the present invention may include positioning means 210 for raising and lowering the hoist 30 to or from a vertical position and a third valve means 220 for controlling said positioning means. The positioning means 210 is connected through the third valve means 220 by conduits between the hydraulic pump 51 and the reservoir 52. The positioning means 210 includes a piston rod 211 attached to the frame-work tower 51 and to a piston 212 in a cylinder 213. Conduits 214 and 215 connect the portions of the cylinder separated by piston 212 to the valve 220.

Operation Initially, the framework of tower 31 rests against abutments 46 when the hoist 30 is released from its travelling position so that the round engaging pads 42 are supported by the ground. Under such initial conditions, the third valve means 220 bypasses hydraulic fluid flow as illustrated in FIG. b directly to the valve 85 which is in its center position as set forth above. To raise the framework tower 31 to a vertical position the third valve means 220 is then positioned as illustrated in FIG. 15a so that hydraulic fluid flows to cylinder 213 so as to project the piston rod 211. When the framework tower 31 reaches its vertical position, third valve means 220 is then returned to its bypassed position illustrated in FIG. 15b so that the framework tower is maintained in this vertical position during and throughout the normal working operation of the power hoist 30. When it is desired to lower the tower 31 from its operative position, shown in FIG. 2 to the travelling position shown in FIG. 1, the third valve means 220 is then changed to the position shown in FIG. 15c so that the piston rod 211 is retracted into cylinder 213 until framework tower 31 rests upon abutments 46.

After the framework tower 31 is in its vertical position, and the platform 33 is resting on the ground with a load on it, the operator may raise the platform 33 by pulling downwardly on the cable length 117 (this motion is possible since the lower egg 118 is below the fork 121). Downward movement of the cable length 117 rotates the control drum 112, and hence the cam shaft 96 in a clockwise direction thus bringing the cam surface 102 against the cam follower 98 and moving the valve spool 89 to its right-hand limiting position. This condition is illustrated in FIG. 9 wherein it will be seen that the valve 85 is placed in a position to intercommunicate the pressure conduit 86 with the outlet conduit '70 which communicates through the flow regulator 68 with the hydraulic motor 53. It will be noted that in this condition, the flow through the regulator 68 is in the reverse direction (as to the regulator) thus forcing the piston 73 upwardly and permitting the full flow that can pass through the orifice 72. The flow just described delivers pressurized fluid through the conduit 69 to the hydraulic motor 53, from whence it is returned through a return conduit 129 to the tank 52. This, in turn, causes powered rotation of the drum 35 in a direction to lift the platform 33 as previously described.

It will be noted that the pressure in the conduit 58 lifts the brake shoe 56 from the drum 35 and also, through the conduit 62, operates the actuating cylinder 63 to open the throttle 65. It will also be noted that should the hydraulic system fail at any time, the pressure in the conduit 58 will drop permitting the spring 57 to engage the brake 55 and hold the platform 33 at its then position along the guides 32. Similarly, such a failure would close the throttle on the prime mover 50 and prevent the same from running away due to a noload condition.

Returning now to the operation of platform 33 in an "upward direction, let it be assumed that the fork 121 reaches the upper egg 119 thus rotating the control drum 112 in a counter-clockwise direction, and moving the cam 101 from its position against the cam follower 98 to its vertical disengage position, illustrated in FIGS. 3 and 10. Referring to the form of the invention, illustrated in FIG. 3, it will be realized that the return of the valve spool 39 to a centralized position under the urging of the spring assembly is damped or slowed down by the dashpot mechanism 102 due to the fact that liquid must be forced from the left-hand side of the piston 103 through the restricted orifice 105 to the righthand side of the piston 103. The just described damp movement of the valve spools 89 gradually cuts off the communication between the pressure conduit 86 and the output conduit 70 so that the fluid delivered to the hydraulic motor 53 is cut off gradually rather than abruptly. It has been found that if the cutoff is gradual over a period of as short as one second or even less, the shock upon stopping the platform is substantially eliminated. On the other hand, if the valve spool were permitted to snap back to central position under the sole control of the spring assembly 90, the stoppage of the platform 33 is not only unduly abrupt but the shock in the hydraulic fluid system is also severe.

In addition to preventing the suddent stoppage of the platform 33, it will be seen that the dashpot 102 imposes a yielding resistance to the movement of the spool 89 to either its left-hand or right-hand position at the time that the cam 101 is manually moved into engagement with the followers 97 or 98. Thus, the operator is prevented from inadvertently jamming the valve 85 into a full speed condition, imposing an undue starting load on the device.

In addition to the automatic stopping at the contact of the fork with the upper egg 19, the platform 33 may be, of course, stopped at any desired position by an operator on the ground lifting on the cable length 117. Also, an operator riding on the platform 33 can, in the usual manner, stop the platform at any desired point by seizing the cable length 117 and lifting the same, or permitting the upward movement of the platform 33 to lift the same.

When it is desired to lower the platform 33, the cable length 117 is lifted further beyond the position to which it is moved by the fork 121 whereupon through the mechanical connections previously described, the cam 101 is rotated counter-clockwise to the left-hand position against cam follower 97 moving the valve spool 89 to its left-hand position and intercommunicating the conduit 70 from the hydraulic motor 53 with the return conduit 87 connected to the tank 52. At the same time, the pressure conduit 86 is connected as shown in FIG. 11 to the output conduit 88 and thus fluid is delivered through the restrictive valve to the tank 52. The pressure built up in the conduit 58 by reason of the restriction posed at the valve 95 is suflicient to release the brake 55 and also open the throttle 65 through the fluid actuated devices 59 and 63 previously described.

The brake 55 having been released, the weight of the platform 33 and any load thereon causes the cable 36 to unwind from the drum 35 which now drives the hydraulic motor causing the same to operate as a pump. When the second valve means 232 is closed and the flow limiting means 200 is open, the motor 53 then receives fluid through the conduit 129 from the tank 52 and pumps the same through the regulator 68, the conduit 70, the valve 85, and the return conduit 87 back to the tank 52. The flow rate through the regulator 68 may be adjusted by means of the adjustment screw 75 as previously described, and is adjusted to give the desired rate of down-travel of the platform. It should be noted that this downward travel rate is substantially uniform and remains approximately the same irrespective of the load on the platform 33 since the rate of down-travel is directly proportional to the rate of fluid flow through the flow regulator 68.

When the present invention is utilized, the flow-limiting means 20th is moved to its closed position and valve means 232 is opened. Under this condition, the flow of fluid through conduit 129 from the tank 52 is reduced. to a very small amount determined by the size of the aperture 204. As already noted, the motor 53 then spins freely permitting the platform 33 to fall at a substantially free fall rate. However, the small amount of flow through the motor 53 is sulficient to lubricate it under these conditions.

Turning now to a consideration of the form of cam operation illustrated in FIGS. 5, 6, and 7, it will be seen that a relatively wide sector cam 134 is provided, the same having rise portions 131 and 132 at opposite ends of the effective cam surface, dwell portions 133 and 134 adjacent the rise portions 131 and 132 and a central high dwell at 135. In this form of cam control no dash-pot is required, the desired graduated operation being accomplished by the cam alone.

The respective positions of the cam 130 and the valve spool 89 during stopping and starting are shown in FIGS. 5, 6 and 7. It will be seen that whenthe cam 139 is rotated for example clockwise to engage the follower roller 98, its first contact moves the spool 89 out of its centralized position and for a short time, blocks all flow through the valve 85. The result of this is to quickly build up pressure in the conduit 58, thus releasing the brake 55 and opening the throttle 65 in the manner previously described. The next successive position of the cam 130 and valve spool 89 is illustrated in FIG. 6 wherein it will be seen that upon reaching the dwell 134, for example, the valve 85 is slightly cracked whereby to permit a highly restricted flow of fluid therethrough. The effect of this is to slowly start the motor 53 (either upwardly or downwardly depending on the left-hand or right-hand position of the spool 89) thus preventing an abrupt start. Such slow speed (about /2 normal speed) continues as long as the cam follower 97 or 98 is engaged with the dwell 133 or 134.

When the cam 130 is now rotated to its limit in either the right-hand or left-hand position, the engaged follower 97 or 98 is lifted onto the high dwell portion 135 Whereupon the valve spool 89 is moved to the full open position as illustrated in FIG. 7 causing the platform 33 to move at full speed.

While the forms of the device shown and described herein are fully capable of achieving the objects and providing the advantages hereinbefore stated it will be realized that they are capable of considerable modification and rearrangement without departure from the spirit of the invention. For this reason, I do not mean to be limited to the forms shown and described but rather to the scope of the appended claims.

I claim:

1. In a power hoist system including:

said

(0) a hydraulic motor connected to said reservoir by conduit means;

(:2) conduit means connecting said hydraulic pump and motor containing a first valve means, said first valve means (I) being connected to said reservoir, and (H) having an up position for raising a hoist in which said hydraulic pump delivers pressurized hydraulic fluid to said hydraulic motor and a down position for lowering said hoist in which said hydraulic motor acts as a pump delivering hydraulic fluid to said reservoir through said first valve means; the improvement comprising a flow limiting means in the conduit between said reservoir and hydraulic motor adapted to restrict the flow of hydraulic fluid to said hydraulic motor when said first valve means is in a down position to an amount suflicient to lubricate said hydraulic motor but insufficient to prevent said hoist from coming down at a rate of substantially free fall.

2. A power hoist system as stated in claim 1 wherein said flow limiting means comprises a gate valve having a small aperture therethrough.

3. A power hoist system as stated in claim 1 which includes a flow regulator in the conduit between said first valve means and hydraulic motor adapted to permit substantially free flow to said hydraulic motor when said first valve means is in an up position and to restrict flow from said hydraulic motor when said first valve means is in a down position whereby said hoist comes down at a regulated rate when the flow to said hydraulic motor is unrestricted.

4. A power hoist system as stated in claim 3 which I includes a second valve means in a parallel conduit between said first valve means and said hydraulic motor adapted to permit free flow from said hydraulic motor to said first valve means.

5. A power hoist system as stated in claim 1 which includes positioning means for raising and lowering said hoist to and from a vertical position and a third valve means for controlling said positioning means, said positioning means being connected through said third valve means by conduits between said hydraulic pump and said reservoir.

6. A power hoist system as stated in claim 5 wherein said positioning means comprises a piston and cylinder attached between the base frame and the frame-work tower portions of said power hoist system.

References titted in the file of this patent UNITED STATES PATENTS 2,407,692 Vickers Sept. 17, 1946 2,869,325 Samuely Jan. 20, 1959 3,036,435 Samuely May 29, 1962 

1. IN A POWER HOIST SYSTEM INCLUDING: (A) A HYDRAULIC PUMP; (B) A RESERVOIR FOR HYDRAULIC FLUID CONNECTED TO SAID PUMP BY CONDUIT MEANS; (C) A HYDRAULIC MOTOR CONNECTED TO SAID RESERVOIR BY CONDUIT MEANS; (D) CONDUIT MEANS CONNECTING SAID HYDRAULIC PUMP AND MOTOR CONTAINING A FIRST VALVE MEANS, SAID FIRST VALVE MEANS (I) BEING CONNECTED TO SAID RESERVOIR, AND (II) HAVING AN "UP" POSITION FOR RAISING A HOIST IN WHICH SAID HYDRAULIC PUMP DELIVERS PRESSURIZED HYDRAULIC FLUID TO SAID HYDRAULIC MOTOR AND A "DOWN" POSITION FOR LOWERING SAID HOIST IN WHICH SAID HYDRAULIC MOTOR ACTS AS A PUMP DELIVERING HYDRAULIC FLUID TO SAID RESERVOIR THROUGH SAID FIRST VALVE MEANS; THE IMPROVEMENT COMPRISING A FLOW LIMITING MEANS IN THE CONDUIT BETWEEN SAID RESERVOIR AND HYDRAULIC MOTOR ADAPTED TO RESTRICT THE FLOW OF HYDRAULIC FLUID TO SAID HYDRAULIC MOTOR WHEN SAID FIRST VALVE MEANS IS IN A "DOWN" POSITION TO AN AMOUNT SUFFICIENT TO LUBRICATE SAID HYDRAULIC MOTOR BUT INSUFFICIENT TO PREVENT SAID HOIST FROM COMING DOWN AT A RATE OF SUBSTANTIALLY FREE FALL. 